Belt assembly

ABSTRACT

A belt assembly which, in operation, can be tensioned along a path, comprising a belt having a toothed surface and a oppositely located back surface and at least one unit fastened to the belt on the side of the back surface. Where the unit is fastened to the belt, parts of the belt are bent out of the path of the belt assembly in the direction of the unit. The unit includes a retention element which engages the toothed surface of the bent belt parts so that a pitch between the teeth of the belt located on either side of the unit is a whole multiple of the teeth pitch of the belt.

BACKGROUND OF THE INVENTION

This invention relates to a belt assembly which, in operation, can betensioned along a path, comprising a belt having a toothed surface andan oppositely located back surface, and one unit or a plurality of unitsfastened to the belt on the side of the back surface.

Such a belt assembly is utilized in practice, for instance inapparatuses for preparing items to be mailed, for the purpose ofconveying postal items located on a transport surface. The unit fastenedto the belt is often a carrier. The carriers extend through the slotsprovided in the transport surface and move forward the postal items tobe conveyed as required, for instance stepwise.

The advantages of a belt assembly over the conveyor chains utilizedheretofore, such as link chains of the bicycle-chain type, areimportant.

Firstly, belts make less noise and are lighter than chains. Owing to thesmaller mass of the belts, the acceleration and retardation forces aresmaller, so that the drives and slip-action clutches can be of lighterconstruction.

Secondly, unlike chains, belts need not be lubricated. Lubricated chainsentail the risk of the postal items becoming dirty.

However, the belts used heretofore in apparatuses for preparing items tobe mailed also have a number of disadvantages which are not inherent toconveyor chains and form an obstacle to the progressive introduction ofthe belt.

The most important disadvantage is the fact that the belts must bemanufactured as endless belts with the carriers provided atpredetermined positions. The carriers are connected to the back surfaceof the belt, for instance by means of glue or by ultrasonic welding, andthe end parts of the belt are similarly connected to each other. Thismeans that both the length of the endless belt and the position of thecarriers are fixed and that for each type of apparatus for preparingitems to be mailed, specific belts must be manufactured and kept instock for service.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a belt assemblywithout the disadvantages described hereinabove.

To that end, the belt assembly of the type mentioned in the preamble ischaracterized in that, in the area of at least one of the unitsmentioned, parts of the belt are bent out of the path of the beltassembly in the direction of the unit, the unit mentioned comprising atleast one retention element which is in engagement with the toothedsurface of the bent belt parts.

As with conveyor chains, units which are attached to the belt in thismanner can be displaced or removed as required. Further, use can be madeof standard commercially available belts without projections formedthereon by welding, which are considerably cheaper than the beltsprovided with projections, to be manufactured in accordance with statedspecifications. Thus, according to the proposal of the presentinvention, a belt assembly is provided which combines the advantages ofnormal conveyor chains with the advantages of the conventional conveyorbelts, with increased flexibility regarding the possible positions ofthe units on the belt and with a substantial reduction of the costprice. In addition, a loose unit provides the advantage of greaterfreedom in construction and the different designs thereof. A furtheradvantage is that the position of the unit can be chosen accuratelybecause it is related to the teeth of the belt. Further, such a unit canbe arranged without special costly tools and, because the retentionelement engages the toothed surface, a firm connection between the beltand the unit can be obtained without the belt having to be clampedtogether at the point of the connection.

In particular when the belt assembly is utilized for positioningoperations, it is particularly favorable when, in accordance with afurther elaboration of the invention, the position of the or eachretention element as well as the contour of parts of the unit againstwhich the back surfaces of the bent belt parts abut are so designed thatthe teeth of portions of the toothed belt adjacent to the unit on eitherside thereof define a toothed profile extending over both belt portions,the pitch between teeth of one belt portion and the other belt portionbeing a whole multiple of the pitch of successive teeth of each beltportion.

Such a belt assembly can be passed over a toothed pulley without anydifficulty, while maintaining the positioning accuracy.

If it is desired that the portion of the toothed belt assembly at thepoint where the unit is located passes through greater angles over atoothed pulley and, in particular, if that pulley moreover has arelatively small diameter, it is advantageous if the contour of parts ofthe unit against which the back surfaces of the bent belt parts abut aremoreover so designed that the pitch between teeth of one belt portionand the other belt portion is also a whole multiple of the pitch ofsuccessive teeth of each belt portion when those belt portions follow apath bent in such a manner that the toothed side of the belt is locatedon the inside.

When bending the belt assembly from a straight path, such that thetoothed side is located on the inside, the neutral plane of the beltassembly, at the point of the unit, forms a continuation of the neutralplane of the belt portions on either side of the unit, and it islocated, in a direction perpendicular to that plane, at the samedistance from the toothed side of the belt, or at least thecontinuations thereof, as the neutral plane of the belt portions oneither side of the unit. This property can be obtained relatively simplywith the belt assembly according to the invention because the beltportions may be bent out of the path at a very slight distance from eachother and thereby the relative displacements of the belt portionsadjacent to the unit upon bending of the belt assembly in the area ofthe unit can be simply adjusted to corresponding relative displacementsupon a comparable bending of an uninterrupted belt portion, through asuitable design of the contours against which the bent belt portionsabut.

As described above, the belt assemblies used heretofore have thedisadvantage that, at least in apparatuses for preparing items to bemailed, they can only be used in endless form. Apart from the objectionthat endless belts must be kept in stock in a variety of matchinglengths and must be especially manufactured to meet the statedspecifications, the assembly and disassembly of endless belts iscumbersome and laborious. Further, in practice the repair of endlessbelts is impossible or possible only with special tools.

In order to circumvent the objections of an endless belt, it isparticularly advantageous when the toothed belt is interrupted and whenbelt end parts on either side of the interruption form the bent beltparts.

The belt end parts can diverge relative to each other in the directionof their ends. This provides the advantage that the distance over whichthe belt end parts as well as the unit project from the back side of theadjacent belt portions can be limited inasmuch as the belt end parts donot project perpendicularly relative to the path determined by the beltportions. Thus, a unit of relatively flat design can be obtained.

A unit of particularly flat design can be obtained if the belt end partsare bent in substantially opposite directions.

When the unit is provided with channels for receiving the belt endparts, these channels comprising open flanks such that the bent belt endparts can be slipped into and out of the unit in both lateraldirections, a very simple method of assembling the unit and the beltparts to be connected thereto is obtained. The connection between twobelt end parts is effected in simple manner by slipping the belt endparts sideways into the channels.

Further, this provides the advantage that it is not necessary for partsof the unit to project in lateral direction beyond the toothed beltparts confined within the unit. Thus, a toothed belt assembly can beobtained which occupies little space in lateral direction. The fact thatthe unit does not project laterally also provides advantages withrespect to the guidance of the belt assembly over a pulley, inparticular when the width of the unit is equal to the width of the belt.

In particular in combination with the channels with open flanks, it is afurther advantage of the above-described diverging course of the beltend parts in the unit, and especially of the oppositely directed courseof the belt end parts in the unit, that the parts of the unit on whichthe supporting contours are provided extend from the mutual connectionbetween them over a slight distance transversely to the path of the beltassembly. As a result, the bending moment exerted on those parts and theconnection between them at a given belt tension is limited accordingly.

In further elaboration of the invention, the unit can comprise acarrier, for instance for moving forward items to be mailed, located ona transport surface.

In an alternative embodiment, the unit can comprise a magnetic detectionelement for determining the position of the unit and hence of the entirebelt assembly.

According to a further elaboration of the invention, the unit comprisesa block-shaped body having a passage of a substantially rectangularcross-section, which extends from an underside facing the belt,substantially perpendicularly to the underside, through the entireblock-shaped body, first sides of the cross-section extendingperpendicularly to the direction of the path of the belt and having alength substantially corresponding to the width of the belt, whilesecond sides of the cross-section have a length such that two belt partshaving their toothed surfaces disposed against each other or a doubledbelt part can be received between the first sides. Further, the unitcomprises means for fixing the belt parts having their toothed surfacesdisposed against each other or a doubled belt part in the rectangularpassage, using a fixing pin serving as a retention element, the fixingpin extending transversely to the direction of the path of the belt,parallel to a belt surface, between the belt parts having their toothedsurfaces disposed against each other or between the legs of a loopformed by the doubled belt part.

Such a unit is suitable for attachment to an uninterrupted belt portion,but also for atttachment to two ends of belt portions for forming acontinuous belt assembly.

According to an alternative further elaboration of the invention, theunit comprises two channels extending from an underside facing the belt,into which retention elements project and in which the bent belt partsare received so as to be form-closed in longitudinal direction. Theretention elements may for instance project from a middle portionbetween the channels, but may also project from a connecting portionbetween parts that support the supporting contours.

With such a unit, no loose parts are necessary, nor any parts projectinglaterally from the belt parts confined in the unit. This unit issuitable for detachably connecting two belt end parts.

At the location of the unit which comprises two channels extending froman underside facing the belt, substantially perpendicularly to thisunderside, in the direction of an upper side of the block-shaped body,and which interconnects two toothed belt end parts, one tooth is missingfrom the substantially continuous toothed profile.

Because, according to a further elaboration of the invention, a centralpost arranged between the channels is provided with an end projectingbeyond the underside of the unit, which end is designed as a tooth ofthe same shape as the teeth of the belt, a continuous toothed profile isalso obtained at the point of the connection between the two beltportions.

The invention may be further embodied in a unit for use in a beltassembly according to the invention, this unit comprising substantiallyoppositely located supporting contours for the parts of a toothed beltthat are bent out of the path of the belt and at least one retentionelement located opposite at least one of those supporting contours, thisretention element being designed for engagement of a toothed surface ofthe bent parts mentioned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of a belt assembly according to theinvention;

FIG. 2 is a longitudinal sectional elevation, taken on line II--II ofFIG. 3, of an embodiment of the unit;

FIG. 3 is a top plan view of the unit shown in FIG. 2;

FIG. 4 is a sectional elevation similar to FIG. 2, where anuninterrupted toothed belt is connected to the unit;

FIG. 5 is a sectional elevation similar to FIG. 2, where an interruptedtoothed belt is connected to the unit;

FIG. 6 is a top plan view of an alternative embodiment;

FIG. 7 is a side elevation of the left-hand side of the unit shown inFIG. 6;

FIG. 8 is a side elevation of the right-hand side of the unit shown inFIG. 6;

FIG. 9 is a second embodiment of an alternative unit with a toothed beltconnected thereto;

FIG. 10 shows a third embodiment of an alternative unit, wherein thefinger is arranged in resilient manner;

FIG. 11 shows a fourth embodiment of an alternative unit, wherein thefinger is pivotally arranged and is pretensioned into the verticalposition via a resilient O-ring.

FIG. 12 shows an elevation of the left-hand side of the unit shown inFIG. 11;

FIG. 13 shows a fifth embodiment of the unit;

FIG. 14 is a side elevation of a sixth embodiment of the belt assemblyaccording to the invention; and

FIG. 15 is an elevation of a unit for use in the belt assembly accordingto FIG. 14, viewed in the direction of the path of the belt.

DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE INVENTION

The exemplary embodiment of the belt assembly shown in FIG. 1 comprisesa finite belt 3 with a plurality of units 1 provided with carriers 2,these units being connected to the belt 3. The unit 1 shown at theright-hand side at the same time connects the two end parts of thefinite belt 3.

It will be clear that the belt 3 can also consist of several finitebelts parts and that these are interconnected by several units of thetype shown in one of FIGS. 2-13. It will also be clear that the belt 3can be an endless belt and that only units 1 of the type shown in FIGS.2-4 are mounted on the belt.

It is noted that the present invention also covers a finite belt withunits mounted thereon.

The units 1, 11 can be provided with carriers 2, 12, for conveyingarticles such as for instance items to be mailed on a transport track T,as well as with magnetic detection elements (not shown), for determiningthe position of the unit 1 or 11 in question or the belt assembly.

The exemplary embodiment of unit 1 shown in FIGS. 2-5 is intended bothfor attachment to a continuous belt part 3 (see FIGS. 2-4) and to aninterrupted belt part (FIG. 5). The unit 1 comprises a block-shaped body4 having a passage 6 of a substantially rectangular cross-section, whichextends from an underside 5 facing the belt 3, substantiallyperpendicularly to the underside 5, through the entire block-shaped body4. The first sides 6a of the cross-section of the passage 6 extendperpendicularly to the direction of the path of the belt 3 and have alength substantially corresponding to the width of the belt 3. Thesecond sides 6b of the cross-section of the passage 6 have a length suchthat two belt parts 3a, 3b having their toothed surfaces disposedagainst each other or a doubled belt part 3ab can be received betweenthe first sides 6a. Further, the unit 1 comprises means 7 for fixing thebelt parts 3a, 3b having their toothed surfaces disposed against eachother or a doubled belt part 3ab in the rectangular passage 6 using afixing pin 9 serving as a retention element. The fixing pin 9 extendstransversely to the main direction of the belt 3, parallel to the beltsurface, between the belt parts having their toothed surfaces disposedagainst each other or between the legs 3b of a loop 3ab formed by thedoubled belt part 3a.

The means 7 for fixing the belt parts having their toothed surfacesdisposed against each other or the doubled belt part 3ab using thefixing pin 9 are formed, in the embodiment shown, by two slots 7 whichare provided in the respective passage walls corresponding with thesecond sides 6b of the cross-section. The slots 7 extend from an upperside 10 of the block-shaped body 4, substantially parallel to thepassage 6 and terminate substantially halfway the passage 6 where theslots 7 form a supporting surface 7a for the fixing pin 9.

The assembly of a unit 1 so designed is very simple. If the unit 1 is tobe mounted on a continuous belt part, first the belt 3 is doubled at thepoint where the unit 1 is to be mounted. Then the loop 3ab formed by thedoubled belt or, in the case of an interrupted belt, the two belt endparts 3a, 3b having their toothed surfaces positioned against eachother, are slipped from the underside 5 of the unit through the passage6 to such an extent that the fixing pin 9 can be fitted at the desiredpoint between the legs 3b of the loop 3ab or between the belt end parts3a, 3b situated against each other. Then the belt 3 and the loop 3abformed thereby or the belt end parts 3a, 3b can be pulled down relativeto the unit 1 until the fixing pin 9 abuts the supporting surfaces 7a ofthe slots 7.

It will be clear that the fixing pin 9 could be accommodated in a bore(not shown) extending transversely to the direction of the path of thebelt and intersecting the passage 6. This, however, renders assembly ofthe unit 1 more difficult because in that case the opening formed by thelegs 3b of the belt loop 3ab or by the belt end parts 3a, 3b locatedagainst each other, must be brought into a position exactly in front ofthis bore before the fixing pin 9 can be introduced.

FIGS. 6-9 show an alternative unit 11 which at the same time serves forthe connection of two belt end parts 13a and 13b, respectively. Such analternative unit 11 is particularly suitable for forming an endless beltassembly from a finite belt assembly.

The alternative unit 11 comprises a block-shaped body 14 having twochannels 17 extending from an underside 15 facing the belt,substantially perpendicularly to this underside 15, in the direction ofan upper side 16 of the block-shaped body 14. The channels 17 extendsubstantially transversely to the direction of the path of the belt 13and are provided with a configuration such that these can receive thebent belt parts 13a, 13b so that the latter are form-closed.

As can be clearly seen in FIG. 6, at the point where the alternativeunit 11 is located, a tooth is missing in the substantially continuoustoothed profile which is determined by the two belt parts 13 extendingon either side of the unit 11. In the embodiment of the alternative unit11 shown in FIG. 9, a depending central post 20 is provided, locatedbetween the channels 17, this central post 20 being provided at thelower end thereof with a tooth 21 of the same shape as the shape of theteeth of the belt parts 13. This tooth 21 replaces the missing tooth inthe substantially continuous toothed profile of the belt, formed by thebelt portions 13. Thus a truly continuous toothed profile is alsoobtained at the point of the connection between the two belt portions13.

The width of the block-shaped body 14 of the alternative unit 11 shownin FIGS. 6-13 substantially corresponds to the width of the belt 13 andthe channels 17 extend over the entire width of the block-shaped body14. When assembling such a unit 11, the belt end parts 13a and 13b cansimply be slipped sideways into the channels 17.

The central post 20 comprises tooth-shaped retention elements 19connected integrally therewith.

In the units 1 and 11, respectively, shown in FIGS. 1-9, the carrier 2and 12, respectively, and the block-shaped body 4 and 14, respectively,are integrally constructed. Such a unit 1 or 11 can be manufacturedsimply and at low cost price.

In connection with calamities, for instance when an operator is caughtbetween a carrier 2 or 12 and any other machine part (not shown), it maybe particularly advantageous when the carrier 2 or 12 of the unit 1 or11 is connected with block-shaped body 4 or 14 for pivotal motion abouta line oriented perpendicularly to the direction of the path of the beltand parallel to the underside 5 or 15 of the unit 1 or 11, and ispretensioned into a vertical position by spring means 22, 23.

In an embodiment of the unit as shown in FIG. 10, the carrier 12 isconnected with the block-shaped body 14 via a thin-walled part 24.Further, the carrier 12 is provided at the lower end thereof with a stop25. In the vertical position of the carrier 12, the stop 25 restsagainst a counterstop 26 which is connected with the block-shaped body14. The block-shaped body 14 and the carrier 12 are in this case made ofa fibre-reinforced plastics, for instance. After the manufacture of sucha unit 11, the carrier is not oriented entirely vertically, but has itsupper side directed in the main direction. By arranging the counterstop26, the carrier 12 is brought into the vertical position. The springmeans are formed by the flexible part 22 which urges the carrier 12 intothe vertical position but which permits the carrier to pivot about theconnection 24 when greater forces are exerted on the carrier.

FIGS. 11 and 12 show another exemplary embodiment of a unit wherein thecarrier 12 is pivotally connected to the block-shaped body 14 via apivot pin 27. In this case, the spring means are formed by an O-ring 23engaging around the lower end of the carrier 12 and the block-shapedbody 14.

It will be clear that the spring constructions shown in FIGS. 9-11 forthe carrier 12 of the alternative units 11 can be used in a similarmanner in the unit shown in FIGS. 1-5.

To prevent forces exerted on the carrier 2 or 12 from causing the unit 1to tilt or giving rise to an undesired deformation of the belt 3 or 13carrying this unit, all units 1 or 11 shown in FIGS. 1-11 are provided,at any rate at a rear side 28 of the block-shaped body 4 or 14, with asupporting member 29 comprising a supporting surface 29a which extendsfrom the block-shaped body 14 in the direction of the path of the beltand aligns with the underside 5 or 15 of the block-shaped body 4 or 14.

When the tension on the belt assembly is very large, there is a risk ofthe channels 17 being bent apart, in particular with the alternativeunits 11 shown in FIGS. 6-12. This can be prevented when, in accordancewith a further elaboration of the invention, a bolt, screw or similarconnecting element 30 is arranged in the block-shaped body 14 andextends in the direction of the path of the belt 13 in such a mannerthat the two bent belt parts 13a, 13b are pierced and the channels 17are squeezed together. Such a construction is shown in FIG. 13.

FIGS. 14 and 15 show a preferential exemplary embodiment of theinvention

This embodiment relates to a unit 31 having a carrier 32 and a body 34.With the unit 31, end parts 33a of belts 33 can be connected to eachother, as appears from FIG. 14.

The unit 31 comprises channels 37 with open flanks having the end parts33a of belts 33 clamped therein. The contours 40, against which rest thebelt end parts 33a, are bent to such an extent as to have portions 40adirected in mutually opposite directions. The belt end parts 33a in thechannels 37 are bent to a corresponding extent, so that the ends thereofalso point in mutually opposite directions.

Owing to this structure, the unit 31 according to this exemplaryembodiment projects only over a slight distance relative to the pathdetermined by the belt parts 33.

The end parts 33a can simply be slipped sideways through the open flanksof the channels 37 into the unit 31 and be clamped, whereupon they areconfined and restrained from displacement in longitudinal directionowing to the retention elements constructed as teeth 39. Being clampedin the channels 37, the belt parts 33a are restrained from lateraldisplacement. A central part 42, which is clamped tightly between teethof the two belt end parts 33a, also contributes to the retention of thebelt portions 33 in both lateral and longitudinal directions, anaccurate positioning being obtained in particular in longitudinaldirection. This last, in turn, is important to obtain a continuous rowof teeth along the toothed surfaces 38 of the belt portions 33, thepitch between teeth of one belt portion 33 and the other belt portion 33always being a whole multiple of the pitch between successive teeth ofeach belt portion.

In combination with the open flanks of the channels 37, the oppositelydirected course of the end parts 33a of the belt parts 33 is moreoveradvantageous because at a given belt tension the bending moment exertedon the parts of the unit that determine the contours 40 is considerablysmaller than in the case where the end parts extend perpendicularly tothe path determined by the belt parts 33 and form arms extendingtransversely to the direction of tension.

The unit 31 according to FIGS. 14 and 15 can be simply manufactured byinjection-moulding from plastics. In order to increase the resistanceagainst deformation upon prolonged loading, the body 34 of the unitcomprises a stiffening rib 43 extending about the channel 37.

The unit 31 further comprises a carrier in the form of a finger 32,integrally formed thereon. In order to prevent the unit 31 from tiltingbackwards when a force is exerted on the finger 32 and to prevent anincrease of the tension in the belt, the unit 31 is provided on one side28 with a supporting member 49 having a supporting surface 49a extendingin the direction of path of the belt and against which the back side ofthe belt 33 abuts when the portions thereof that are adjacent to theunit 31 on either side thereof are tensioned in a straight path.

Backward tilting of the unit 31 is further prevented in that the finger32 is not arranged centrally but at a greater distance from thesupporting member 49. Also the relatively great length of the unit 31 inthe direction of the path, obtained through the partly oppositedirection of the channels 37, contributes to an effective support of theunit against backward tilt.

Instead of having a substantially oppositely directed configuration, thecontours 40 and the end parts 33a of the belt parts 33 may also haveconfigurations that diverge relatively to each other, away from the pathdetermined by the belt portions. In that case, too, compared with anembodiment where the contours and the belt portions are directedperpendicularly to the path determined by the belt portions, a flatterconstruction of the unit and a reduction of the bending moments exertedon the parts of the unit that carry the contours 40. However, the effectachieved is then smaller than in the case of the embodiment of theinvention shown in FIGS. 14 and 15.

It will be clear that the present invention is not limited to theembodiments described, but that various modifications are possiblewithin the scope of the invention.

I claim:
 1. A belt assembly which, in operation, can be tensioned alonga belt path, comprising a belt having a toothed surface and anoppositely located back surface, and at least one unit fastened to thebelt on the side of the back surface, wherein, in the area of the atleast one unit, parts of the belt are bent out of the path of the beltassembly in the direction of the unit and said unit comprises a contouragainst which the back surfaces of the bent belt parts abut and includesat least one retention element which is in engagement with the toothedsurface of the bent belt parts, the retention elements and the contourpositioning the belt parts so that teeth of portions of the toothed belton either side of the unit define a toothed profile extending over bothbelt portions across the unit, a distance between teeth of one beltportion and teeth of the other belt portion being a whole multiple ofthe pitch of successive teeth of each belt portion, wherein the unitcomprises two channels extending from an underside facing the belt, intowhich channels the retention elements project and in which the bent beltparts are received so as to be form-closed in a longitudinal direction.2. A unit to be attached to a belt assembly having a toothed belt,comprising substantially oppositely arranged supporting contours forparts of the toothed belt which are bent out of a belt path and at leastone retention element located opposite at least one of said supportingcontours for engagement of a toothed surface of the said bent parts, thesupporting contours being shaped to diverge in substantially oppositedirections wherein at least part of the bent belt is supported in aposition parallel to the belt path.
 3. A unit according to claim 2 wherethe supporting contours include channels for receiving belt end parts,which channels are provided with open flanks, such that the bent beltend parts can be slipped into and out of the unit in both lateraldirections.
 4. A unit according to claim 2, further comprising acarrier.
 5. A unit according to claim 4, wherein the carrier forms anintegral part of the unit.
 6. A unit according to claim 4, furthercomprising a supporting member comprising a supporting surface whichpartly determines an underside of the unit that faces the path of thebelt in operating condition and constitutes a continuation of one of thesupporting contours, such that it abuts the back side of the belt whenthe portions of the belt adjacent to the unit on either side thereof aretensioned along a straight path.
 7. A belt assembly which, in operation,can be tensioned along a belt path, comprising a belt having a toothedsurface and an oppositely located back surface, and at least one unitfastened to the belt on the side of the back surface, wherein, in thearea of the at least one unit, parts of the belt are bent out of thepath of the belt assembly in the direction of the unit and said unitcomprises a contour against which the back surfaces of the bent beltparts abut and at least one retention element which is in engagementwith the toothed surface of the bent belt parts, the retention elementsand the contour positioning the belt parts so that teeth of portions ofthe toothed belt on either side of the unit define a toothed profileextending over both belt portions across the unit, the pitch betweenteeth of one belt portion and teeth of the other belt portion being awhole multiple of the pitch of successive teeth of each beltportion;wherein the toothed belt is interrupted and belt end parts oneither side of the interruption constitute the bent belt parts; whereinthe belt end parts are bent in substantially opposite directions.